Does the National Library have any primary sources relating to Twm Sion Cati?
Ateb
The National Library does hold Twm Sion Cati's will. A digitised version of the will is also available to view online.
Follow the link below to search the Wills:
https://discover.library.wales/primo-explore/search?vid=44WHELF_NLW_NUI&lang=en_US
And search under Twm Sion Cati's real name: Thomas Johnes, 1609 (Ref: SD1609-20).